Crimping process



1968' G. R. CLARKE, JR 3,406,436

GRIMPING PROCESS Filed Nov. 30, 1965 v INVENTOR GEORGE R.CLARKE,JR.

ATTORNEY United States Patent F ABSTRACT: on THE DISCLOSURE A: processfor regulating the crimp frequency of compaction-crimped yarn. Uncrimpedyarn is fed into a stuffer box at a constant rate and emerges in'theform of a plug from which crimped yarn is taken up at a constant rate.The crimp frequency (crimps per inch) imparted to the yarn in thestuffer box inversely determines the distance downstream from thedischarge port at which the crimped yarnunfolds from the plug. Thisdistance (and hence also the crimp frequency) can be kept within a fixedcontrol region by controlling the amount of resistance offered by thegate ofthe stuflier box to the compressive force of the compacted yarntherewithin, e.g., by varying the weight placed on the gate.

This invention relates to a process for crimping a strand or multiple ofstrands of fibers. More particularly, this invention relates to aprocess for controlling the crimping of synthetic fibers, e.g. nylon, sothat the crimp frequency, in terms of 'crimps per inch, is uniformthroughout the yarn.

Compression crimping has recently been used on a large scale to impartto synthetic or man-made fibers, e.g. thermoplastic yarn, a bulk orcrimp giving the appearance of a wool-like fiber. In the known processesof compaction crimping, e.g. Those using a stutfer box, the yarn socrimped is characterized by some lack of uniformity in crimp frequencythroughout the length of the yarn. Specifically, artificial man-madefibers, e.g. nylon, which after being spun are drawn to orient thepolymer molecules, are characterized by a relatively smooth surfacewhichis crimped'to give the'yarn a wool-like appearance using, in manycommercial operations, a stutfer box. Generally, this process isperformed by feeding the'y'arn in a semi-plastic state through nip rollswhich impart a nip to the fiber. The yarn passes through the nip rollsinto a box called a stuifer box wherein it' is "compacted withpreviously advanced yarn under compaction and the unoccupied yolume ofthe stuffer box is maintained at a minimum using a discharge'gate whichresists egress of the yarn and thus determines' the compaction of theyarn. The yarn is taken up by conventional winders on conventionalbobbins, or the like,"at a rate less than the feed'rate of theyarn'tothe stuffer box through the'nip rolls. Many factorsin fluencethebehavior of the yarn in a stuffer box, which determine the degree ofcrimp imparted to it and the crimp frequency. For instance, it has beenfound that in com mercial operation using a'sta'ndard-stuffer box thatthe crimp frequency can varyusing the .same feed rate of yarn throughthe nip rolls, the ,same stuffer box, same temperatures and the sametake 'up ,rate. The reason for these'changes in crimp frequency it notknown .but it is believed that processing conditions pres nt in thepolymerizin'g, spinning and drawing operations effect the yarn behaviorin the crimping step so as to change the crimp frequency to a differentvalue. It is also believed that water present in the form of atmosphericmoisture may also effect the crimp frequency. However, by far themajority of reasons for variations in crimp frequency at constantprocess conditions are still unknown.

It has been proposed to maintain the crimp frequency 3,406,436 PatentedOct. 22, 1968 constant by varying the feed rate of the yarn into thestuffer box via the nip rolls together with adjusting the take-up rate,thus maintaining a substantially constant degree of compaction of theyarn within the stuffer box. This method of control of crimp frequencyis not desirable in that it involves a substantial number of movingparts in the apparatus employed to achieve the regulation of feed andtake-up. It also suffers from the disadvantage that when the feed rateof the yarn to the stuffer box is decreased to a level below the normalprocess operating rate there is a decrease in the amount of crimped yarnproduced per given unit time. Also, when the take-up rate is decreasedto keep the crimp frequency uniform an increase in duration of fiberexposure to heat treatment results which may cause fibernon-uniformities, It is therefore desirable to maintain the crimpfrequency constant while keeping the feed rate of uncrimped yarnconstant and, at the same time, maintaining a constant take-up rate offreshlycrimped yarn.

It is the object of this invention, therefore, to provide a process forcrimping yarn wherein the crimp frequency is maintained constant in theyarn despite the presence of the aforementioned unknown factors whichinfluence crimp frequency.

It is still another object of this invention, therefore, to

' provide such process for crimping nylon or other synthetic yarn in aneconomical manner whereby the yarn s0 crimped is characterized by a highdegree of uniformity of crimp frequency.

It is still another object to provide a process for crimping yarn bycompaction to provide uniformity of crimp frequency in the yarn whereinthe feed rate of the yarn to the zone of compaction and the take-up rateof winders, etc. are maintained constant.

These and other objects of this invention will become apparent from thefollowing complete description of my invention, accompanying drawing andappended claims.

This invention contemplates a process for regulating the crimp frequencyof compaction-crimped yarn, said process comprising: crimping the yarnin a zone of compaction so as to form a plug, maintaining an unfoldingpoint of the yarn from the plug within a predetermined region by varyingthe resistance of the zone of compaction against the yarn therein whilemaintaining the feed rate of the yarn to the zone of compaction and thetake-up rate of the yarn from the plug constant.

My process is preferably performed by passing uncrirnped yarn, e.g.nylon into a conventional staffer box or other confined region having amovable wall or gate, with weights attached to the gate to adjust itspressure against the yarn within the stuffer box, thereby adjusting theresistance of the zone of compaction against the yarn. Different yarns,because of processing conditions, contribute different resistanceagainst the zone of compaction, thereby necessitating greater or lessergate pressure.

In a preferred embodiment of my invention, the yarn is withdrawn fromthe zone of compaction in the form of a plug, e.g. on a conveyor beltand taken up downstream from the zone of compaction.

More specifically, my process is directed to controlling the crimpfrequency by controlling the unfolding point of the yarn from the yarnplug which issues from the discharge end of the stuffer box on, forexample, a standard endless conveyor belt. When, due to the unknownfactors effecting crimp frequency, the unfolding point of the yarn fromthe plug, which is selected to be within an arbitrary control region,but is dependent upon feed rate and take-up rate, moves upstream, it isan indication, as I have discovered, of an increase in crimp frequency.On the other hand, I have also discovered that when the unfolding pointof the yarn from the plug moves downstream of this arbitrarily selectedcontrol region for the tion ofa decrease in crimp frequency.-I havefurther-discovered that the unfolding point of the yarn from the plugcan be maintained within a predetermined region, and hence the crimpfrequency can be kept generally constant by controlling the force on theupper stuifer box gate'acting against the compacted yarn. As a result,there is a substantially constant total volume of yarn in the stuiferbox. Crimping yarn with an essentially constant yarn plug unfoldingpoint as herein prescribed insures, uniform crimp. It will be observedthat according to my process the crimp frequency of the yarn ismaintained uniform without adjusting the yarn feed rate to the stuiferbox or the rate at which the yarn is withdrawn from the plug form.

My invention will be more readily understood by reference to theaccompanying drawing which is a side view of a stulfer box partiallybroken away wherein 2 is the overall stuffer box into which yarn 4 isfed via nip rolls 6 and 8. Gate 10 which is bounded by sides 12 and 14and is hinged at 16 using pin 18. The gate has afiixed thereto verticalbar 20 on which weight 22 and 24 are placed. The yarn so crimped withinstuflfer box 2 by compaction issues at discharge port 26 onto endlessconveyor belt 28 moved by rolls 30 and 32 which are driven by a motor(not shown). The crimped yarn unfolds from the yarn plug at some point Ain the accompanying drawing. When, because of conditions which affectscrimp frequency, the yarn unfolding point changes from con trol point Ato point B there is observed, as discussed above, an increase in crimpfrequency. To account for this, sufiicient weight is taken off gate 10,thereby increasing the volume of the stuifer box and decreasing thecrimp frequency, to adjust it to the frequency desired and thereby causethe unfolding point of the yarn to move back downstream toward point A.When, on the other hand, the unfolding point moves downstream from pointA say to point C, suificient weight is applied to gate 10 over verticalbar 20 to bring the unfolding point back upstream toward point A. If theunfolding point is allowed to remain at point C, a lower crimp frequencythan desired is imparted to the yarn.

It will be realized that my process can be performed at any temperaturesuitable for crimping of the yarn involved, feed rate of yarn to stuiferbox, take-up rate of yarn from plug form, etc., and using other types ofapparatus for crimping by compaction. It should also be realized thatvarious means for regulating the force exerted on the stuffer box gatecan suitably be employed. These include use of a pneumatic cylinder inwhich the air pressure is regulated to give the desired force on thestuffer box gate; and standard spring mechanisms adjustable by a screwwhereby the different tensions of the spring cause different forces tobe exerted upon the stuifer box gate.

In order to illustrate in detail the nature and manner of practicing myinvention, the following example is presented.

20 ends of 1050 denier, 70 filament, /2 Z twist polycaproamide (Nylon 6)at a temperature of 90 C. were fed into a stuffer box similar to thatshown in the accompanying drawing at a feed rate of 1425 ft./minute andwound-up on a yarn package at 1160 ft./minute. The gate pressure wasvaried during the process run to vary the resistance against the yarn,thereby maintaining substantially constant yarn volume in the stufferbox. The weights placed on the stuifer varied between 1.5 lbs. and 5.0lbs. The yarn received a uniform crimp having 14 crimps/inch controlledwithin 12.0 crimp/inch on 20 separate stuifer box units for severalmonths. Necessity for continuous tests by quality control labs waseliminated due to the crimp process of this invention.

It will be realized that my invention can be utilized in -other'crimping processes, e.g. jet crimping with or without pre-chemicaltreatment, gear crimping, etc. The method of controlling the CIimpin thecase of jet crimping involves maintaining a pair of micro-switches orother sensing means, one proximatethe jet and the other downstream fromthe desired unfolding point, but within the zone of compaction. If theplugmovesdownstream, it actuates the, microswitch' which adjusts presurevia the jet against the yarn. If the plug backs up, it. actuates theswitch proximate the jet to decrease pressure against the yarn. In thecase of gear crimping, the crimp is regulated by increase or decrease,of pressure on the yarn via the gears. This can be done using weights oradjustable spring loaded means which apply tensionto-the' yarn via thegears. In the case of knife-edge crimping, the weightor pressureresistance is maintained by adjusting the position laterally of theknife-edge against the yarn. I

It. can vbe readily seen from the above that I have provided a new anduseful processfor controllingcrimp frequency of yarn crimped bycompaction. It is-seen that my process can be easily performed, does notnecessitate large expenditures for equipment anddoes not require anycutting down periodically in production rate.

The terms and expressionswhich have been employed are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, to exclude any equivalents of the.features shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. 1

What is claimed is: I

1. A process for regulating the crimp frequency of compaction-crimpedyarn comprising:

(a) feeding yarn to a zone of compaction at a constant rate;

(b) crimping the yarn in the zone of compactionso as toform a plug; Y

(c) withdrawing the plug from the zone of compaction; and I (d) takingup the crimped yarn from the plug at a constant rate, and at a distancefrom the zone of compaction which is kept within a fixed control regionby varying the resistanceof the zone of compaction to the yarn therein.

2. A process according to claim lwherein:

an increase in the distance of the control region from the zone ofcompaction is reversed by increasing the resistance .of the zone ofcompaction to the yarn therein; and

a decrease in the distance of the control region from the zone ofcompaction is reversed by decreasing the resistance of the zone ofcornpaction to theyarn therein., I

3. A process according to claim 2 wherein the plug is withdrawn from thezone of compaction on .a conveyor belt. p

4. A, processaccording toclaim .2 wherein theresistance of the Zone ofcompaction is varied utilizing weights. r

5. A process accordingto claim 2 wherein the yarn isnylonf I j p IReferences Cited s -UNITED STATES'PATENTS LOUIS K. RIMRODT, PrimaryExaminer.

